New World Screwworm Fly Found in Texas Threatens Cattle Industry

The New World screwworm fly, known for its flesh-eating larvae, has been confirmed in south Texas, according to the U.S. Department of Agriculture (USDA). This marks the first instance in decades where the parasite poses a threat to the U.S. cattle industry. The detection occurred in a 3-week-old calf in La Pryor, Texas, roughly 50 miles from the Mexico border.

Quarantine Measures and Inspection

To prevent the spread, Texas State Veterinarian Bud Dinges has implemented a 12-mile quarantine zone. Movement of any warm-blooded animals, including pets, is restricted without inspection. Agriculture Secretary Brooke Rollins emphasized that no other screwworm fly detections have been reported in the U.S.

Impact on Livestock and Past Concerns

The fly’s larvae pose a threat to livestock, although they don’t infest food. Affected animals, with proper treatment, can recover. Officials recall substantial economic losses in the past due to the fly, which was eradicated in the 1970s. Rollins noted this is the first case in Texas since 1966.

Control and Prevention Efforts

Efforts to keep the screwworm fly out of the U.S. include releasing sterile flies to mate with wild females, inhibiting population growth. USDA’s preparations ensure no mass infestation is anticipated. Rollins expressed confidence that the current situation won’t establish the pest permanently in the U.S.

Background on Screwworm Flies

The New World Screwworm fly is tropical, previously affecting cattle across the southern U.S. and confined to Panama until 2024. Females lay eggs in wounds or mucous membranes, hatching larvae that consume flesh. This makes them distinct among fly species, affecting livestock, pets, wildlife, and occasionally humans. Untreated infestations can be fatal.

Recent U.S. Cases

A case was confirmed in Maryland in August 2025 following travel to El Salvador. No U.S. transmission was detected. Earlier, an outbreak occurred in the Florida Keys in 2016, primarily affecting wild deer, which was contained by early 2017.

Future Preventive Strategies

Efforts to control screwworm flies include converting a Mexican fruit-fly facility to breed sterile screwworm flies, establishing a fly dispersal center in southern Texas, and planning a new $750 million fly factory. The USDA has deployed 8,000 fly traps and tested extensive fly and animal samples. Rollins has also restricted livestock imports from Mexico to contain the spread.

Community Cooperation

Dinges urged ranchers and pet owners to respect the quarantine, preventing further pest movement. Proper adherence to these measures can help contain and eventually eliminate the threat.

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